It has become increasingly common to provide sewage pumpout stations for boats at docks. In such installations, a pumpout pump is provided which is connected up to a sewage holding tank (typically of plastic) in the boat, and quickly pumps all of the sewage out of the tank. Most commercial pumps for these pumpout stations have a capacity of up 10 to about 40 gallons per minute (151 liters per minute), although capacities of as high as 170 liters per minute may be expected in the future. When such pumps are operated, it is difficult for the pump operator to know exactly when all the sewage has been pumped out of the holding tank, and the pump may stay in operation for a significant period of time, often up to about 30 seconds, after the tank has already been emptied. It has been recognized that this can exert a substantial strain on the holding tank, and can result in damage to the tank, or an implosion. Damage to the tank may result in leakage of sewage into the environment, obviously a highly undesirable event.
According to the present invention, an assembly is provided which solves the problem of possible holding tank damage as a result of rapid pumpout of the sewage from the tank at a dockside pumpout station. According to the present invention, vacuum relief is provided, typically in the form of a vent check valve, in the holding tank to prevent implosion or other damage to the tank associated with rapid pumpout through an outlet conduit and pumpout fitting. The vacuum relief means is capable of providing sufficient air flow into the holding tank so that if the holding tank is emptied by a 170 liter per minute pump remaining in operation for 30 seconds after the plastic holding tank has been emptied, no damage to the holding tank ensues.
The vent check valve utilized in the practice of the present invention preferably comprises a conventional vent check valve including a valve body, a reciprocal valve element, and a coil spring engaging the valve element and biasing the valve element so that it is in sealing relationship with the valve body. The coil spring has a spring constant sufficient to prevent the valve element from moving to an open position as a result of the boat hull being subjected to rough water.
The holding tank also typically includes an indicator of the fullness (e.g. at least an indicator of three-quarters fullness of the tank), and a gas vent, which typically is connected to a gas filter. Also, the tank outlet conduit can include in addition to a first branch which has a dockside pumpout fitting, a second branch connected to a pump within the boat, which in turn is connected to a seacock for discharge in open water where environmental regulations permit.
The vent check valve also typically provides means for guiding movement of the valve element with respect to the valve body from a sealing position engaging the valve body and preventing passage of fluid (ambient air) from outside the holding tank through the valve to inside the tank, to an open position allowing passage of fluid (air) from outside of the holding tank through the valve to inside the tank.
The valve body element may include an interior surface mounting a first sealing ring (such as a quad ring), and the valve element includes an axially elongated substantially cylindrical peripheral surface, the peripheral surface engaging the sealing ring in the sealing position. Typically the valve element includes a top and a bottom, with the peripheral surface extending between the top and the bottom. The top has a tapered peripheral edge portion of a smaller diameter than the cylindrical peripheral surface, and the bottom includes an annular ledge having a larger diameter than the substantially cylindrical peripheral surface, and for engaging the valve body to stop movement of the valve element, under the bias of the biasing means, in the sealing position.
The valve body may have an outer peripheral substantially cylindrical surface having at least one sealing ring (such as an O-ring, or a pair of O-rings) mounted thereby, and an external diameter. The holding tank comprises a top surface having a tubular element therein having an inner surface with an inner diameter slightly greater than the external diameter of the valve body outer peripheral surface. The valve body outer peripheral surface is disposed within the tubular element with the O-rings in sealing engaging the tubular element inner surface.
The means for guiding movement of the valve element preferably comprises: A shaft portion of the valve element substantially concentric with and extending upwardly away from the valve element substantially cylindrical peripheral surface. A spider disposed within the valve body interior surface, spaced from the second sealing ring. And, a collar connected to the spider, the collar receiving the shaft portion therein and guiding reciprocation of the shaft portion. Preferably the biasing means comprises: A coil spring having first and second ends thereof, and wherein the valve element further comprises a screw threaded end part of the shaft portion and a nut screw threaded thereon so that the position of the nut with respect to the valve element elongated peripheral cylindrical surface may be adjusted. And, wherein the coil spring first end engages the spider and the coil spring second end engages the nut, the coil spring being compressed between the nut and the spider.
The invention comprises both a boat assembly where the holding tank and other elements are mounted within the boat hull, and a sewage holding tank assembly per se which typically is used in a boat but may also be used in a recreational vehicle or the like.
It is a primary object of the present invention to provide a desirable holding tank assembly with vacuum relief, most desirably for use in a boat. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and the appended claims.